Integrated circuit devices containing one or more embedded oscillators are ubiquitous in the art. Such embedded on-chip oscillators often require trimming. For example, the oscillation frequency of an oscillator may vary from one device to another within a given production lot due to variations in manufacturing conditions (e.g., process, voltage and temperature (PVT) variations). The trimming is performed to ensure, within practical limitations, that the oscillators on all devices of a particular lot exhibit the same oscillation frequency (also referred to herein as oscillator frequency). Conventional approaches to the oscillator trimming process usually consume relatively large amounts of time during production testing, as explained in more detail below.
In conventional oscillator trimming techniques, automated test equipment (“ATE” or a “tester”) external to the device under test (DUT) first configures the DUT so that the oscillator output signal is provided at an externally accessible terminal of the DUT. Then, the tester loads, successively into a trim register on the DUT, each one of a set of trim values that are to be tested. The oscillation frequency, that is, the frequency of the oscillator output signal, depends on the trim value in the trim register. The tester may use linear sweep searching, successive approximation searching, or a combination of both, to select the trim values to be tested.
For each trim value loaded into the trim register, the tester measures the corresponding oscillation frequency of the oscillator via the aforementioned externally accessible terminal of the DUT. Depending on the range of oscillation frequencies that may be expected from the oscillator, and depending on the frequency measurement capability of the tester, the oscillation frequency being measured may need to be divided down, either internally on the DUT or on a tester board that interfaces with the tester. Based on the frequency measurements taken for the corresponding trim values loaded, the tester identifies the trim value that sets the oscillator frequency closest to a target value.
The aforementioned frequency measurements can be rather time intensive, especially if the oscillator signal is noisy, such that each measurement needs to be averaged over multiple periods of the oscillator, or averaged over a period of time. The test time problem is further compounded if: the set of trim values to be tested is large; and/or there are multiple oscillators to be trimmed; and/or the transfer characteristic (input trim value versus output frequency) of one or more oscillators is not monotonic, and thus requires the tester to use a more complex trim algorithm that takes even more time to execute.
It is desirable in view of the foregoing to provide for reducing the time required to trim on-chip oscillators.